Most often you may be confused about 2 look-alike light green or dark green invasive weeds in your garden. These two plants were confusing for me also when I was an undergraduate student. They are yellow nutsedge and purple nutsedge. Nutsedges are green perennial weeds that grow in wild conditions as well as gardens, lawns and crop fields. In Bangladesh, these weeds are mainly found in low lands especially in paddy fields. Scientific names of yellow nutsedge and purple nutsedges are Cyperus esculentus and Cyperus rotundus respectively. Origin of nutsedges is likely to be Africa and Asia but it grows almost all over the world including the USA and the European countries now and has a negative impact on crop production.
Nutsedges are usually perennial plants and they like hot humid sunny conditions. Though in cool temperature they may be appeared as dead and their leaves lose their green color but their tuber remains dormant in the soil. Their modified stems (tuber and rhizomes) can go down up to 15 inches in the soil. Both yellow and purple nutsedge like wet soils but they also grow in dry soils. So, you can find these green grass like weeds in your gardens or lawns as well as in paddy fields. Both yellow and purple nutsedge can regrow from rhizomes and tubers. Nutsedges can also reproduce and spread through seeds. In cooler regions yellow nutsedge is likely to be more common than look alike purple nutsedge. Purple nutsedge is usually more aggressive than yellow nutsedge.
Taxonomic classification of yellow nutsedge and purple nutsedge
| Taxonomic Category | Yellow Nutsedge | Purple Nutsedge |
| Kingdom: | Plantae | |
| Phylum | Spermatophyta | |
| Subphylum | Angiosperms | |
| Class | Monocotyledonae | |
| Order: | Cyperales | |
| Family: | Cyperaceae | |
| Genus: | Cyperus | |
| Species: | Cyperus esculentus | Cyperus rotundus |
Are yellow nutsedge and purple nutsedge grasses?
Yellow nutsedge and purple nutsedge are two different plants and they are not grasses. But as they look like grasses they are often known as nutgrass. Their eradication is often difficult. How can you differentiate between grasses and sedges? The stems of sedges have different look than grasses. Sedges have triangular dark green or light green stems in cross-section and are not hollow. On the other hand, stems of grasses are usually round in cross-section and are hollow. Thicker leaves also differentiate sedges from grasses. Nutsedges are usually taller than most grasses. Stems of most grasses are dark green like yellow nutsedge but purple nutsedge have light green stems.
Yellow nutsedge vs purple nutsedge
Purple nutsedge plant grows up to 6 inches and yellow nutsedge can grow up to 15 inches.
Leaves of both yellow and purple nutsedge look like grass leaves. But like grass leaves nutsedge leaves have no collars, ligules or auricles. They have thicker leaves than grasses. In cross section nutsedge leaves look like V-shaped. Leaves have pointed tips. Leaf color of yellow nutsedge is dark light green while purple nutsedge have dark green leaves.
Leaf width of yellow nutsedge is usually between 5-10mm. On the other hand, Purple nutsedge leaves are 4-7mm wide.
Nutsedges usually start flowering after 4-6 weeks of emergence. Flowers in the heads are small and are arranged in spikes attached to the flower stack. Each flower forms single fruit with a single seed.
Yellow nutsedge have yellow or golden yellow flower heads.
Purple nutsedge have dark brown or purple colored flower heads.
How to control yellow and purple nutsedge?
These aggressive look-alike sedges are weeds in your flower gardens, vegetable gardens, lawns and in crop fields. They can be controlled by different methods which include chemical control and cultural practices. Sustainable control is not so easy when it is not controlled in the early infestation. You may not be able to kill yellow nutsedge or purple nutsedge with herbicides that are recommended for grass control. Tubers of nutsedges are often called nutlets. A single nutlet of nutsedge is enough to produce hundreds of shoots.
It is very difficult to control nutsedges only by cultural or chemical control. Excessive use of chemical herbicides is harmful to the environment. Combined approaches of cultural, mechanical and chemical control have the most effective possibility of effectively controlling nutsedge.
Cultural and mechanical control of nutsedges:
- Both yellow nutsedge and purple nutsedge love wet soil. So, do not let the soil get over moisture in your garden or lawn. Do not water your plants in gardens frequently.
- Check the drainage system in your gardens or lawns. The poor drainage system in gardens or lawns causes wet soil conditions and wetland weeds like yellow or purple nutsedge can easily grow there.
- Deep watering lawn with time interval may be a good practice for controlling nutsedges and other weeds. If you water deeply with proper time interval the upper soil will get the time to dry up.
- If the soil in your garden or lawn is wet and you see yellow or purple nutsedge there drying up the soil will not kill them because after growing in wet conditions nutsedges can survive in drought conditions. So, check the moisture condition of your garden or lawn even though there is no nutsedge there.
- If you are planning to buy soil for your gardens or lawns, be sure that the soil is from a yellow or purple nutsedge free area.
- Before buying any plant for your garden or lawn, make sure the soil at the base of the plant is free of nutsedge seeds or tubers.
- Take care of the desired plants and grasses in your gardens or lawns. Pests or diseases may cause bare areas in your gardens or lawns that may help yellow or purple nutsedge to establish.
- Nutsedge tubers are good source of spreading them. Cultural operations can spread nutsedge tubers from single location to whole garden or lawn. Tubers can remain dormant in soil for years. So, be careful about that.
- Before buying new sods for your garden or lawn be sure that they are free from nutsedge tubers.
- Before using garden tools and equipment, wash them carefully so that they don’t carry seeds or tubers of nutsedges or other weeds.
- Maintain recommended pH for sods so that they can compete with sedges and other weeds.
- Apply recommended dose of fertilizer timely for sods or grasses in lawns or gardens.
- If you find purple or yellow nutsedge in your lawn with seeds, do not mow before removing them. Mower blade may spread seeds nutsedges in your lawn.
- Usually, Nutshede plants do not grow in dark, they do not love shade. So, take care of desired grasses and other plants so that they create shady condition for nutsedges. Without required sunlight nutshade will lose its vigour.
- If you remove only the above ground green portion of yellow nutsedge or purple nutsedge with flowers, they will come again as their tubers and rhizomes spread horizontally and vertically below soil. So, dig the soil and remove the parts to get rid of them and this is the only way of mechanical control of both yellow and purple nutsedge.
Chemical control of nutsedge
- You can use some post emergent herbicides to control yellow or purple nutsedge.
- Read the label with the herbicide package to make sure that it is effective in controlling nutsedge and not harmful to the desired grasses or other plants in your gardens or lawns. Also be sure about residual effect of the chemical if you have to apply that in your vegetable garden. Keep herbicides and all harmful chemicals in safe places so that children or pets cannot reach there. Use eye shields and other recommended protective shields to protect yourself while spraying herbicide.
- Post emergence herbicides are absorbed mainly by leaves. So, make sure that the nutsedge are in actively growing stage with adequate leaves open. Water your garden or lawn before spraying the herbicide.
- As the herbicide will be absorbed by the foliage, do not mow your lawn before spraying the herbicide as mowing will shorten nutsedge leaves. Moreover, mowing will spread seeds of nutsedge to the whole lawn.
- Herbicides containing Bentazon, Imazaquin, Halosulfuron or Sulfentrazone can kill yellow and purple nutsedge.
- For vegetable and fruit gardens Pelargonic acid, d-limonene, Acetic Acid, Bentazon or Glyphosate containing herbicides may be used. But be sure that the used herbicide will not harm your vegetable or fruit plants.